I can feel the passion and heat! Work possibly on the imagery, let me have more of an image. I know it sounds silly but set up the setting, where and what's going around. What the room looks like, how the air feels on their body. It sounds silly but will add to the reader's interaction with the story. Think about diction, possibly.
Your defiantly on a beautiful level with the sex though
Constructive comments aside this is a REALLY good story, I'm genuinely impressed
continue on.
4.5 stars.